7. PROJECT SUMMARY Background. Electro- and magneto-encephalographic (EEG/MEG) responses to a stimulus are systematically attenuated? by up to 80%? if the same stimulus was presented less than 8-12 seconds ago. This dynamic modulation of response amplitude to identical stimuli is one of the most striking and fundamental properties of the EEG/MEG signal. The proposed work will test the hypotheses (1) that the attenuation of EEG/MEG amplitude to repeated identical stimuli is caused by short-term synaptic depression at cortical synapses and (2) that the manifestation of synaptic depression at the micro- and meso-scopic level critically depends on local circuit and network architecture leading to a complex but systematic relationship between macroscopic modulation of EEG/MEG responses and several micro- and mesoscopic measures of neural function.